Tidewater Glaciers

A glacier meets the sea
Hubbard Glacier in Wrangell-St Elias National Park and Preserve is the longest tidewater glacier in North America at 70 miles in length.


If a glacier is fed by enough snow to flow out of the mountains and down to the sea, we call it a tidewater glacier—the type many people come to Glacier Bay and Kenai Fjords to see. These types of glaciers will break off or calve into saltwater at sea level, and a few others that reach the sea at high tide only. The show can be spectacular. As water undermines some ice fronts, great blocks of ice up to 200 feet high break loose and crash into the water.

When tidewater glaciers calve icebergs into the marine environment, they serve as pupping and molting habitat for some of the largest seasonal aggregations of harbor seals in Alaska. Although tidewater glaciers are naturally dynamic, advancing and retreating in response to local climatic and fjord conditions, most of the ice sheets that feed tidewater glaciers in Alaska are thinning and, as a result, many of the tidewater glaciers are retreating. Climate change models predict rapid loss of glacier ice with unknown impacts to seals that rely on tidewater glacial habitat.

Glaciers and Climate Change

Most of Alaska's glaciers have been retreating over the last century, and research shows that the rate of recession has increased significantly in recent years. The effects of melting glaciers impact freshwater flow, vegetation, and coastal marine ecosystems.

Glacial meltwater from tidewater glaciers has chemical properties that can exacerbate ocean acidification. Freshwater inputs and cold water tend to decrease ocean pH and increase acidification. This acidification can have adverse effects on marine wildlife habitat and populations.

Learn more about tidewater glaciers

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    Last updated: July 27, 2017